Reasons for frequent falling off of refractory castables at kiln mouth
1. The negative pressure at the kiln head reflects the balance between the air used in the kiln and the hot air entering the kiln head cover. Generally, the kiln head exhaust fan increases the exhaust volume, and the negative pressure at the kiln head increases, and vice versa. The hazards of positive pressure at the kiln head are mainly manifested in: flying sand and hot smoke from the kiln head gap, easy burning of the kiln head seal, damage to the kiln door and aggravated wear of the kiln head cover, and in severe cases, the kiln head cover will be burned down; positive pressure can easily cause damage to peripheral equipment, inability to see the fire at the kiln head, and personal injury caused by splashing high-temperature materials. As mentioned above, the kiln head pressure is affected by the exhaust volume of the kiln head and kiln tail exhaust fans. In the same production line, the kiln ventilation volume is relatively unchanged, and the kiln clinker needs to be cooled to a reasonable temperature. That is to say, when the system is designed and matched, the capacity of the kiln head exhaust fan cannot be too small, otherwise the remaining cooling air volume has nowhere to be discharged.
2. Kiln system operation rate The comprehensive operation rate of the kiln system represents all issues such as whether the production is normal, whether the management is fine and stable, and the frequency of fault shutdown. Under normal circumstances, the comprehensive operation rate of the kiln system reaches 85% and is basically normal, and more than 90% is considered normal production, indicating that the production line has less unplanned maintenance. The refractory materials of the kiln system are most damaged by the kiln shutdown. The kiln mouth refractory castables is the most seriously damaged part of the kiln shutdown. The higher the comprehensive operation rate of the kiln, the longer the life. If there is an accident such as the shrinkage and blockage of the decomposition furnace, the surface temperature of the kiln mouth lining will drop from about 1400℃ to 100~200℃ in more than 10 hours. After the blockage, it needs to be quickly heated to normal temperature. Such strong alternation of cold and hot is repeated, and the internal structure of the kiln mouth castable is damaged, easy to break and fall off, which has a great negative effect on the service life.
3. Kiln mouth iron guard structure The kiln mouth structure is generally composed of a cylinder, iron guard and castable. The purpose of setting up the kiln mouth guard iron is to effectively protect the kiln mouth cylinder section made of ordinary steel to avoid high temperature flue gas burning. The two are connected and fixed together by 4 bolts to form a whole. The guard iron relies on the protection of the castable to reduce the working temperature and abrasion, and ensure the stability of the structure. The deformation of the kiln head cylinder leads to large vibration and the loosening of the guard iron bolts are important reasons for the fall of the kiln mouth castable.
4. The influence of castable quality and pouring construction quality There are many problems in construction quality control. The structure of the anchor nail is unreasonable, the welding at the intersection is not standardized, and it is easy to melt at high temperature; the anchor nail is single-angle, with fewer welding surfaces and not easy to weld firmly; the layout of the anchor nail is unscientific, with many blind spots, especially the refractory castables above the guard plate and the retaining brick ring cannot be pulled. The importance of leaving expansion joints during pouring is not fully understood, and too few or no expansion joints are left in actual construction, which leads to the extrusion and bursting of the kiln mouth castable. In order to save time and meet the construction schedule, the formwork is not supported, and the operation point is moved from 7 or 9 o'clock in the circumference to 6 o'clock for construction, resulting in the castable being loose and not dense. The mixing is not standardized, and water is added before the dry material is fully mixed. Considering the convenience of construction and the influence of construction time, the mixing method is to increase the amount of water and use the flowing material to pour while mixing. The mixing and molding time are not well coordinated, resulting in the mixed castable not being used in time. The pouring vibration is uneven, and the phenomenon of long vibration or heavy vibration is prominent. Affected by the urgency of production, the short curing time is also very damaging to the castable.
5. The influence of the kiln mouth retaining brick ring The service life of the kiln mouth refractory castables and the integrity of the kiln mouth retaining brick ring are the biggest factors among many factors. The burning of the kiln mouth retaining brick ring forms an inverted triangle, and the kiln bricks will directly squeeze the kiln mouth castable, resulting in a large area of kiln mouth castable extrusion and shedding, and the kiln is forced to stop. Combined with the kiln mouth guard iron castable shedding accidents that have occurred many times in our company in the past year and a half, the kiln mouth retaining brick ring is the first to bear the brunt. Once the kiln mouth retaining brick ring is burned, it must be replaced as soon as possible.
